Corrosion-Fatigue Cracking in Al 7075 Alloys

: An investigation was carried out to characterize the effect of aging, environment (include [NaCl] concentration), and load ratio on fatigue crack growth kinetics of Al 7075 alloy. The materials investigated were peakaged Al 7075-T651 and overaged Al 7075-T7351. The results indicate: (1) the fatigue crack growth rates and fatigue crack growth threshold, Kth, for Al 7075-T651 and Al 7075-T7351 are comparable at similar stress ratios in each of the three test environments (vacuum, ambient air, and 1% NaCl solution); (2) irrespective of Al 7075 aging conditions and stress ratios, the fatigue crack growth rates are lowest in vacuum, followed by those in ambient air, and are highest in 1% NaCl; (3) for both Al 7075-T651 and Al 7075-T7351, the fatigue crack growth rates initially increase rapidly when [NaCl] increases from 0.001 to 1% and then remain unchanged when [NaCl] further increases from 1 to 15%; and (4) for both Al 7075-T651 and Al 7075-T7351, the fatigue crack growth rates are higher at higher stress ratio in all three environments and the Kth progressively decreases as the load ratio increases.